Roll-up doors are commonly used to close openings, such as large doorways. For example, roll-up doors have been used to provide barriers between separate rooms of a warehouse or to provide closures for dock openings. Roll-up doors provide a closure mechanism that can be opened and closed to allow for passage of people or vehicles through the opening. Because of their high-speed operation, roll-up doors are particularly preferred when high-speed vehicles, such as forklifts, will be passing through the opening.
Roll-up doors typically include a roll of material positioned above a doorway, and a bottom beam secured to the free end of the material. The bottom beam is typically biased downwardly (e.g., using cables, pulleys and weights or springs) to keep the material under tension and to assist in unwinding of the roll. The roll is driven by a motor that selectively unwinds and winds the roll to close and open the doorway, respectively.
Recently, roll-up doors have been designed so that the bottom beam will break away upon impact by a force above a predetermined limit. Such a design limits damage to the assembly in the event that a vehicle (e.g., a forklift) inadvertently collides with the bottom beam. The breakaway feature is accomplished by detachably connecting both ends of the bottom beam to respective guide members (e.g., called "tension arms") that are at least partially hidden within vertical tracks along the doorway jambs. For example, the bottom beam can have a transverse opening in each end of the beam (i.e., extending through the plane of the beam) that receive pegs extending from the guide members. The pegs are releasably held within the transverse openings by a corresponding detent mechanism, and the guide members are biased downwardly to provide tension to the material. Upon being impacted by a sufficient force, the beam will break away from the pegs, thereby reducing the likelihood of damaging the assembly.
Roll-up doors can further include a mechanism for biasing the roll in the winding direction (i.e. biasing the door upward) to at least partially counteract the weight of the unwound material to thereby assist the motor in winding the roll. In addition, roll-up doors can further include retention straps secured to the guide members and wrapped around the roll to prevent the guide members from slamming to the ground when the bottom beam breaks away from the guide members.
The above-described types of roll-up doors have performed satisfactorily under a variety of circumstances. However, there has been a need for simpler, less costly and more reliable roll-up doors.